This invention relates to a rigid connection of structural parts and a tool and a method for establishing the connection, in an arrangement with a first hollow tubular member structural part and a second structural part surrounding the first structural part and utilizing a high internal pressure forming technique.
A connection of this type and a tool of this type are known from German Patent Document DE 39 27 896 A1. A connection and a tool are described there for the positionally accurate fastening of cams on a hollow shaft. In the machining position, the cams and the hollow shaft which is guided through their threading opening are placed in a corresponding, negative-shape engraving of a forming tool divided into halves or quarters. An oblong, elastically deformable container, which is open on one side and into which a pressure fluid is filled, is introduced into the hollow shaft in a pressurized manner. In the area of one end of the hollow shaft, the container is supported on a bearing of the tool and, on the other end, it is supported in a fluid-tight and pressure-tight manner to a mouthpiece of a hydraulic system. The mouthpiece rests against the deforming tool and in the process supports the hollow shaft on this end. The mouthpiece, which is constructed as a pressure introducing body, has a pressure intensifier piston by means of which the hydraulic system by way of a pressure duct provided in the mouthpiece and leading into the container exercises a high pressure on the pressure fluid, whereby the elastically deformable container expands and is placed against the interior side of the hollow shaft. By means of a further pressure rise, the hydraulic pressure is transmitted by way of the container to the hollow shaft which, as a result, is radially expanded along its whole length so that, because of the circumferential enlargement, the cams are provided with a press fit on the hollow shaft. However, for establishing the connection when the vehicle body parts are already coated during the assembly, the tool designed for this purpose is completely unsuitable because of the high-expenditure insertion of the structural parts into the tool, the multi-part construction of the tool which requires a plurality of operating steps, and the very high space requirement of the tool. Because of the high demands on the uniformity of the expansion of the hollow shaft--therefore, of the interior structural part--whose surface quality must be very high with a view to a sufficient concentricity, for establishing of the connection, a complete encapsulation of the structural parts to be connected is required by means of the known tool which is not possible in the case of vehicle body parts by means of acceptable expenditures.
Furthermore, it is known from German Patent Document DE 30 08 840 C2 to manufacture a tube frame construction of a motor vehicle by means of a point welding, seam welding, folding or gluing of metal half shells.
In vehicle body construction, the sheet metal parts are generally connected with one another at their joining points in the body in white by means of resistance welding, as known, for example, from German Patent Document DE 33 06 397. As an alternative thereof, mechanical connections, such as penetration joining is used, as illustrated in a representative manner by German Patent Document DE 37 01 895. In this case, for avoiding corrosion in the customer operation, the vehicle body parts are subjected to an anticorrosion coating after the establishment of the connection. However, in order to join vehicle body parts during the assembly which are ready to be installed and therefore achieve a customer-friendly formation of variants in the final assembly which takes into account individual wishes, joining processes, such as welding and penetration joining cannot be used because in this case, the coating would be destroyed at the joining points and the visible side of the vehicle body parts would be visually impaired because of indentations, distortions of material and discolorations.
It is an object of the invention to further develop a connection of the above-mentioned type and a tool and method for establishing the connection such that the structural parts as vehicle body parts can also be joined after a coating during the assembly in a simple manner and can be effectively fixed to one another without any plastic deformation of the exterior structural part and without damage to the coating and thus without a visual impairment of the visible side of the structural parts.
According to the invention, this object is achieved by providing an assembly of structural parts for a motor vehicle comprising a first hollow part, and a second hollow part surrounding and fixedly connected to the first hollow part by internal high pressure expansion of the first hollow part, said first hollow part including inwardly protruding projections which form a releasable plug in connection with the second hollow part during a preassembly operation before internal high pressure expansion of the first hollow part, and said first hollow part being configured to plastically deform in response to internal high pressure to form a permanent connection with the second hollow part with substantially no plastic deformation of the first hollow part.
According to the invention, it is permitted that, during the assembly of the structural parts, because of the construction of the exterior second structural part with reduced cross-sections, a tentatively releasable connection between the structural parts is obtained by a simple fitting of the structural parts into one another, in the case of which releasable connection a given adjusted position of the structural parts with respect to one another is temporarily secured. The interior first structural part is supported on the cross-sectional reduction sections while, in the course between the sections, it forms an expansion space with the surrounding exterior structural part into which it can be plastically deformed when high pressure is introduced by way of a fluid. By means of the therefore achieved form-fitting between the structural parts, the previously releasable plug-type connection will become unreleasably rigid. Because of the fact that the fluid is held in a flexible hollow body introduced into the interior structural part and a dry deforming of the interior structural part is achieved. As a result of the different deforming capacities of the structural parts which are caused by different materials and/or different wall thicknesses of the structural parts, the interior structural part which, because of the significantly lower yield tension, is easier to deform than the exterior structural part, can be plastically deformed under high fluid pressure, whereas the exterior structural part remains undeformed or is deformed no more than elastically. Thus, the deforming is concentrated only on the interior structural part so that the exterior structural part, particularly its visible side, is not deformed and therefore has no unattractive bulges. Likewise, in this case, a chipping of the coating is avoided, for example, of the paint coat or of the corrosion protection.
The tool used for the fixing of the two structural parts to one another which is virtually constructed as a bending-elastic, radially flexible, hollow rod, can be inserted into any bending shapes of structural parts under a fluid pressure which is exercised on the inside and which is above the atmospheric pressure. In this case the tool adapts to the course of the interior of the interior first structural part because of its fluidically generated bending elasticity. In this case, the introduced tool can be pushed in a variable manner more or less far into the interior structural part, depending on at which point an expansion space of the exterior structural part is situated. In order to essentially prevent an axial lengthening of the tool when the fluid pressure is applied, which axial lengthening, on the one hand, results in a disturbance of the radial expansion of the interior structural part and, on the other hand, results in a considerable danger of tearing the skin of the rod-like swelling body, tension devices are provided which counteract in the axial direction. The swelling body is closed on all sides in a pressure-tight manner and completely closes the interior structural part on its ends so that, when a high fluid pressure is applied, no bubble of the elastic swelling body is formed which pushes between the interior and the exterior structural part and which may burst, whereupon a rapid pressure drop will occur in the high-pressure fluid.
The deforming takes place by means of very low equipment expenditures because an exterior support for the structural part situated on the outside as well as the press bedplate and the press slide customary in generally known internal high-pressure deforming arrangements are completely eliminated. The need for such parts is eliminated by the special construction of the invention and the material characteristics of the exterior structural part, on the one hand, and the largely free deformability of the interior structural part, that is, the absence of increased demands with respect to the surface quality and the course of the interior structural part, on the other hand. At the same time, the tool for the internal high-pressure deforming is not fixed stationarily but can be handled manually or possibly by means of an assembly robot in a locally independent manner.
By means of the possibility acquired by means of the connection according to the invention of incorporating, shortly before the finishing of the vehicle by means of finished and coated structural parts still changes into the body of the motor vehicle, the most varied model variants can be constructed on a short-term basis and in a rapid manner without any losses of quality according to customers' wishes.